1. Field of the Invention
This invention relates to the fabrication of thin film magnetic read/write heads and particularly to a method for forming a slider surface so that the read/write head is less subject to thermal asperities due to near contact with a magnetic disk.
2. Description of the Related Art
As shown in FIG. 1, a hard disk drive (HDD) uses an encapsulated, small thin film magnetic read/write head (40), formed on a ceramic substrate (75) to read and write data on a magnetic medium or storage disk (1). The read/write head is formed using well known semiconductor deposition techniques such as electroplating, CVD (chemical vapor deposition) and photolithographic patterning and etching. The entire structure of head plus substrate is called a slider (10). FIG. 1 is a schematic illustration of such a device as is used in the prior art and whose performance improvement is the object of the present invention. The slider (10) has a pre-patterned air-bearing surface (ABS) (42), (43) that faces the rotating disk (1) during HDD operation. The slider is mounted on the distal end of a head gimbal assembly (HGA) (not shown) that is activated by an electro-mechanical mechanism and control circuitry to position the head at various positions along the magnetic tracks on the disk (not shown).
As the disk is rapidly rotated by a spindle motor (not shown), hydrodynamic pressure causes an air flow between the ABS of the slider and the surface of the disk. This flow lifts the slider so that it literally flies above the surface of the disk (at a “fly height”) on a layer of air. The spacing between the head and the disk surface at this position is referred to as the magnetic spacing (80). The edge of the slider into which the disk rotates (indicated by an arrow) is called its “leading edge (30),” the opposite edge, which contains the read/write head (40), is called the “trailing edge (50).”The read/write elements (40) are encapsulated within the read/write head portion (45) of the slider. The head portion (45) is formed on the slider substrate (75) at an interfacial plane (65). The slider substrate has an ABS plane (42) and the read/write head has an ABS plane (43). These two planes are parallel but the read/write head ABS plane is slightly lower than the substrate ABS plane as shown in the figure. The aerodynamics of the slider motion lifts the leading edge higher above the rotating disk surface than the trailing edge.
The slider substrate (75), is composed of hard AlTiC. Sputtered Al2O3 (alumina), formed to a thickness of approximately 0.035 mm, forms a nearly transparent insulating coating (55) on the ABS surface and encapsulates the read and write sensors (40) which are located at the trailing edge of the slider. We will note again the interfacial plane (65) between the AlTiC of the substrate body (75) and the sputtered alumina (55) that covers the read/write head components.
There are many factors, both internal and external to the drive that can directly or indirectly affect the magnetic spacing during HDD operation. For example, if the drive is subjected to an external shock, the shock can be transmitted to the head causing a modulation in the magnetic spacing. Such a modulation can progress to a head-disk contact, damaging the head or disk or both and, if severe enough, causing a failure of the drive. Other reasons for variations in the magnetic spacing are such internal problems as variation in disk smoothness, surface contamination, stiction, or high-altitude drive operation.
Another major problem that results from magnetic spacing variations during disk drive operation is thermal “asperities,” variations in read head operation that result from its deviations from thermal equilibrium. The read transducer portion of the read/write head is typically made up of a magnetoresistive (MR) element that is encapsulated in exotic materials. When the read head comes into contact with any mechanical asperity on the disk (e.g. a surface irregularity, dirt, an accumulation of lubricant, etc.), a resulting development of frictional resistance will produce a signal spike of approximately 1-3 microsecond duration, in the MR read element which will inhibit its reading capabilities. FIG. 2 is a schematic side view of the slider mounted read/write head (40) flying above a rotating disk (1), the arrow indicating the motion of the disk surface towards the read/write head. Two exemplary “bumps” (70) on the disk would undoubtedly cause sufficient head-disk interaction to create an undesirable thermal asperity.
Even some of the next generation technologies, such as dynamic write excitation during the write operation of the disk drive, create a head-disk contact problem. By exciting the writer, we intentionally cause the transducer to protrude, reducing the magnetic spacing and thus increasing the chance of head-disk contact. The problem becomes even more of a concern in perpendicular magnetic recording (PMR), where the writer structure includes a much larger volume of material.
Much research and effort has been invested in both head development and disk development to address the problem of head-disk contact. Improvements ranging from smooth disks to textured media, coupled with micro-texturing of the slider surface and new and complex designs of the air-bearing surface (ABS) of the heads have helped to alleviate the problem to a large extent. However, both head and media manufacturers recognize the need for continual improvement in this area and that recognition is has led to a conscious effort to discover methods of achieving that goal.
Numerous approaches have been taken in the prior art to address the problem of head-disk interactions. Haddock et al. (U.S. Pat. No. 6,243,234 B1) propose an approach that recesses the entire transducer area within the slider. While this certainly addresses the problem, the amount of recession suggested, approximately 40 nm, is very large and will reduce the efficiency of the head. Also, this type of solution requires very tight process control in creating the recession, and such process control is a constant challenge in manufacturing. Another potential problem associated with this approach is due to the nature of the hardness variations of the writer and reader materials, which would cause localized profile variations that would adversely affect the head operation.
Another approach is taught by Boutaghou et al. (U.S. Pat. No. 6,556,389 B1), which is to recess the entire transducer area much below the substrate and to cover it with a thick, insulative covering. This coating, together with the slider, is then coated yet again with another wear resistant coating, such as a diamond-like carbon (DLC) coating to supply double protection. This does help to reduce the effects caused by a head-disk contact, but it requires a multiplicity of complicated process steps and, therefore, lowers the manufacturing efficiency. Boutaghou also proposes an alternative approach in U.S. Pat. No. 6,233,118 B1, where a debris-collecting feature is engraved in front of the transducers, to prevent or reduce the thermal asperities due to head-disk contact. All of these ideas suggest the necessity of additional process steps to build protective features into the head, thereby increasing the cost of manufacturing.
Tian et al. (U.S. Pat. No. 5,768,055) attacks the problem in an innovative fashion, by placing the protective DLC coating onto the slider body in the form of an array so as to potentially reduce the probability of thermal asperities caused by a head-disk contact. This placement and design of this array must be carefully and accurately calculated, depending upon the fly height characteristics of the head. This approach, therefore, also warrants additional processing steps and masks which, in turn, increase manufacturing costs.
Riddering et al. (U.S. Pat. No. 6,359,754 B1) suggests depositing the protective coating on the head in a way that avoids the actual transducer element. This causes an offset that, in turn, creates a step-like difference in surface height between the transducer and the slider body, thereby providing additional protection to the head during an event. This approach runs the risk of allowing metallic elements in the transducers to corrode, since they lack the necessary protection of a coating. With the next generation of metals being considered for use in head fabrication, the potential for corrosion is even increased.
Another interesting approach to reducing thermal asperities due to head-disk contact is physically building patterns and features in front of transducers. This approach, in various forms, is the subject of inventions by Kameyama et al. (U.S. Pat. No. 6,891,699 B2), Kasamatsu et al. (U.S. Pat. No. 6,903,901 B2) and Otsuka et al., (U.S. Pat. No. 6,728,069 B2). All of these inventions require additional process steps which raise the manufacturing cost of the slider. For example, U.S. Pat. No. 6,903,901 teaches processes such as reactive ion etch (RIE), ion milling and photolithography to produce protective elements on both the leading and trailing edges of the slider surface.
The present invention attacks the asperity problem by using a CMP polishing method previously developed by the inventors and described in their application entitled: “Method And Apparatus For Producing Micro-Texture On A Slider Substrate Using Chemical & Mechanical Polishing Techniques,” Ser. No. 11/378,100, now U.S. Pat. No. 7,513,820 B2, Filing Date Mar. 16, 2006, which is fully incorporated herein by reference. This method, which will be applied in a novel manner described fully below, uses the lapping process by which the ABS of the slider is polished to create a protective ridge that will eliminate thermal asperities caused by head-disk interactions.
The initial step in slider fabrication is the slicing of a wafer on which is formed a plurality of slider mounted read/write heads into pre-patterned blocks or “quads,” (quadrants) which are then further sliced into individual rows containing a horizontal array of slider mounted read/write heads. After this cutting is completed, the ABS of the row is polished by lapping to obtain critical dimensional control of the read and write elements as well as for the improvement of the surface finish. Polishing is typically accomplished by applying an abrasive slurry to the surface being polished. Such slurries are well known in the prior art and several exemplary patents are noted herein as being representative of the slurry compound and the method of its application. For example, Sato et al. (U.S. Pat. No. 6,722,962, Zuniga et al. (U.S. Pat. No. 6,312,316), Takahashi et al. (U.S. Pat. No. 6,312,316) and Fontana, Jr., et al. (U.S. Pat. No. 6,131,271) all teach CMP slurries containing colloidal silica and KOH. Wong et al. (U.S. Pat. No. 6,117,499 discloses a method for texturing a magnetic disk surface by the use of a combination of laser application and KOH slurry CMP.
Based on the above discussion of prior art, it would be extremely advantageous to develop an efficient, easy-to-implement (within present manufacturing processes) and inexpensive method of protecting a slider mounted read/write head from the problem of thermal asperities produced by head-disk interactions. The method taught in the present invention has distinct advantages over the prior art cited above and achieves the desired goal. The objects of the present method and the means of achieving those objects will now be presented.